The fox squirrel (Sciurus niger) is native to the eastern half of the United States. This tree squirrel was introduced into cities, large private estates and campuses in the West where they have thrived, often to the detriment of the western grey squirrel. In the West, rarely have fox squirrels extended their range into surrounding forests and rural areas.
Also commonly called an eastern red squirrel, the fox squirrel is chiefly arboreal, but does spend more time on the ground than other tree squirrels.
The largest species of tree squirrel native to North America, fox squirrels have four toes on the front feet, five toes on the rear and sharp claws. There is great variation in coloration within this species. In some areas the upper parts are rusty or reddish grey while the lower parts are yellowish or orange. At the other extreme are fox squirrels that are mostly grey with a little orange on the legs and black heads or even totally steel grey or black with no rust at all. All fox squirrels have short ears and long, bushy tails. They do not have internal cheek pouches.
Fox squirrel habitat is open forest with little undergrowth, or ideally a small stand of trees amid agricultural land. However, these mammals adapt well to urban environments. They are diurnal and non-territorial.
The diet of a fox squirrel depends on their location – various nuts, seeds, acorns, grain crops, fruits, berries and the buds of deciduous trees. Although fox squirrels do not hibernate, they do store some acorns or other food.
Usually solitary except during the breeding season, fox squirrels use two types of nests. In the summer they construct leaf and stick platform nests in the forks of deciduous trees. Winter or breeding nests are usually natural cavities in trees or abandoned bird holes, although occasionally fox squirrels will excavate their own nest. The gestation period is 45 days. The young are blind and helpless with no fur at birth. At 4 to 5 weeks the eyes open and the ears open at 6 weeks. Between 12 to 14 weeks the young fox squirrels are weaned with total self-support occurring at about 16 weeks. There are usually two litters of 3 or 4 pups a year.
Fox squirrels eat acorns which are high in tannins. Poisonous to worms, the tannins help keep the squirrels free of tapeworms and roundworms.
Fox squirrels accumulate porphyrins in their teeth and bones. (Porphyrins are naturally occurring, water-soluble, nitrogenous biological pigments such as hemoglobin and chlorophyll.) These accumulated porphyrins cause fox squirrel teeth and bones to appear pink or bright red under UV light. Interestingly other tree squirrels, even if they eat the same diet, do not accumulate porphyrins.
Leonard and I recently enjoyed watching this fox squirrel near the Eucalyptus Grove on the University of California Berkeley Campus.